Galvanometer-based optical scanners are specialized motors that typically have a mirror attached to an end of a shaft. Typically, galvanometer-based optical scanners must limit the range of rotation angles of a rotor. At some specific angle, the torque produced by the motor becomes zero. Thus, if the rotor of the motor ever comes to rest in that position and the turning force is zero, the rotor will become immobile or stuck and thus unable to rotate out of the stuck position. Further, a position sensor only responds to a limited range of angles and will not produce a valid signal when operated outside of that range of angles. Yet further, in order to reduce mirror inertia as much as possible, X and Y mirrors used in a scanning system must be placed very close to each other. If operated outside a preselected scanning range, there are some angles at which the X and Y mirrors will collide with each other, resulting in mirror destruction.
There is a need to restrict the rotor to a valid range of angles. As a result, manufacturers of known galvanometers have generally used one of three approaches including drilling a hole through an output shaft or position sensor shaft, and placing a stopping pin into the shaft, wherein the stopping pin engages an external plastic or rubber bumper when the galvanometer is operated outside a desired scanning range. Other known systems have allowed the moving element of the position sensor to collide with an internal rubber bumper, or a mirror mount is allowed to collide with an external metal or plastic bumper.
There are problems with known approaches. In the first case described above where a hole is drilled in the shaft, and where such is also most common, the hole weakens the shaft which lowers shaft stiffness and increases problems related to resonant frequencies. Having to operate with such an undesirable arrangement even if the stop is not used is clearly undesirable. In the second case described above, where the moving element of the position sensor collides with an internal rubber bumper, such collisions may bend the position sensing element, or fatigue the bond between the position sensing element and the position sensing shaft. This affects long term repeatability of the scanner. Yet further in the third case described above, such a technique can only be used when a mirror mount is used, and can not be used when the mirror is directly bonded to a shaft, as is common with low-inertia scanners.